How does the author use metaphor in the novel, The Ten Loves of Nishino?

The vacant lot in which Shiori buries things serves as a symbol of sadness. The lot is the one place where Shiori, as well as Nishino, feel a sense of solace and secrecy. The lot protects them from the world beyond. Metaphorically, the lot is a proverbial graveyard of the characters' sadness and sorrows.